Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
PUBLISHED CHANGEABLE MESSAGE SIGN MESSAGE DESIGN AND DISPLAY GUIDELINES FOR INCIDENTS AND ROADWORK The first comprehensive set of guidelines for designing and displaying CMS messages for incidents and roadwork was documented in the Human Factors Requirements for Real- Time Motorist Information Displays, Vol. 1âDesign Guide (2) in 1978. The design guide was written following extensive human factors laboratory, controlled field, and operational studies. The emphasis in the report was on (1) the recom- mended content of CMS messages for various traffic situations; (2) the manner in which messages should be displayed (format, coding, style, length, load, redundancy, and the number of repetitions); and (3) where messages should be displayed with respect to the situations they explain. Following additional human factors laboratory, controlled field, and operational studies, the 1978 Design Guide was updated in a 1986 report, Manual on Real-Time Motorist In- formation Displays (3). A 1991 report, Guidelines on the Use of Changeable Message Signs (4), provided guidance on (1) selection of the appropriate type of CMS display, (2) the design and maintenance of CMSs to improve conspicuity (target value) and motorist reception of messages, and (3) pitfalls to be avoided. CMS technology developments after 1986 were emphasized. In 1997, the New Jersey DOT funded a multiyear re- search study that included human factors laboratory and controlled field studies dealing with CMS message design and operations. The research led to the development of the 2001 Variable Message Sign Operations Manual (5). The report includes detailed step-by-step processes for designing messages for incident and roadwork situations and includes CMS operational policies. It provides very specific informa- tion for CMS operators and entry-level personnel, reminders for experienced personnel, and high-level information for managers. The 2004 FHWA Changeable Message Sign Operation and Messaging Handbook (6), an updated and expanded version of the New Jersey study (5), was written for national use with added emphasis on CMS policy and operational procedures. The design and display of messages on CMSs introduce many challenges to transportation agencies. Recommendations to 8 meet these challenges were presented in this handbook. In addition, a few operational practices were discussed with respect to conformance and nonconformance to recommended message design and display options that are based on human factors studies. Texas DOTâs (TxDOTâs) 2006 Dynamic Message Sign Message Design and Display Manual (7) is patterned after the New Jersey DOTâs Variable Message Sign Operations Man- ual and FHWAâS Changeable Message Sign Operation and Messaging Handbook. To date, TxDOTâs manual includes the latest objective data and information that meets the specific needs of TxDOT. DEFINITIONS AND CHANGEABLE MESSAGE SIGN MESSAGE DESIGN CONSIDERATIONS Developing Effective Changeable Message Sign Messages To be effective, a CMS must communicate a meaningful message that can be read and understood by motorists within a very short time period (constrained by the sight distance characteristics of the location and design features of the CMS). Effective message design involves recognition of the basic principles for the following (2â7): â¢ Message content, â¢ Message length, â¢ Message load and units of information (informational unit), â¢ Message format, and â¢ Message splitting. Message Content Message content refers to specific information displayed on a CMS. Essentially, the key elements are: what is wrong ahead and what the motorist should do about it. If CMSs are to be read and believed by motorists, the content of the message must provide information relative to their needs. Above all, motorists want to know if something âaheadâ has occurred on the roadway that would change their plans. A CMS message should also present âadvice.â This ap- pears at the end of the brief message. It may be REDUCE SPEED, EXIT AND TAKE OTHER ROUTES, or some other advice. CHAPTER TWO CHANGEABLE MESSAGE SIGN MESSAGE DESIGN AND DISPLAY GUIDELINES AND POLICIES
or while in stopped traffic reading a sign or billboard. However, drivers cannot always devote full attention to sign reading; they must share their attention between information necessary for the task of driving and the information on signs. Because of this time-sharing situation, it will take longer to read a sign than if the driver could devote all of their attention to the sign. It is important to note that unfamiliar drivers must typically read the entire message on a CMS to properly comprehend the information being presented. In contrast, they do not have to read the entire guide sign to obtain relevant information about guidance. Therefore, it takes a driver longer to read a CMS message than to read the message on a guide sign. In a driving situation, the driver has a limited amount of time to read a message on a sign. He or she can start reading a sign when the words become legible at the legibility distance of the sign. Guidelines recommend that the character height on CMSs on freeways should be at least 450 mm (18 in.) so that drivers can read and comprehend typical CMS messages while traveling at typical freeway speeds. The legibility dis- tances that should be used when designing and displaying messages on CMSs with characters that are 450 mm (18 in.) high are shown in Table 1 (5â7). About 85% of drivers can begin reading a message on the newer light-emitting diode (LED) CMSs with 450 mm (18-in.) charactersâdesirable on freewaysâabout 245 m (800 ft) in front of the sign (8). Research strongly suggests that motorists can read an 8-word message (excluding prepositions such as TO and AT) in 8 s, or one word per second (2â10). Based on the known legibility distance of CMSs, this translates to the following maximum message lengths (11â13): â¢ Eight words while the motorist is traveling at 90 km/h (55 mph), â¢ Seven words at 105 km/h (65 mph), and â¢ Six words at 115 km/h (70 mph). Longer messages than these should be avoided because motorists will often reduce their speeds in order to read the message or will simply not read the entire message. When the complexity of the driving situation increases owing to extremes in geometrics, heavier traffic volumes, 9 Many motorists will ignore advice unless a reason is of- fered for taking it. The âreasonâ in most cases is the problem (e.g., MAJOR ACCIDENT, LEFT 2 LANES CLOSED). Motorists expect this information to appear first in a CMS mes- sage. They also would like to know where the problem has occurred. This is given on the second line. If the incident occurs far away, it may not affect them if they planned to exit long before then. Message Length Message length refers to either the number of words or the number of characters and spaces in a CMS message. With CMS line capacity less than optimal, it becomes necessary to count the characters in a message to determine if the message will fit. If the message does not fit, acceptable abbreviations can be used and/or redundant words can be eliminated. It may, at times, be necessary to split the message and display the parts in two phases. The maximum length of a CMS message is controlled in part by reading timeâthe time the motorist has available to read the message. Reading time is affected by (1) the time that the motorist is within the legibility zone of the CMS message, and (2) by the amount of activity in the traffic stream to which the motorist must attend (e.g., reading signs, adjust- ing vehicle speed, and lane positioning). The entire message must be short enough to allow motorists to glance at the sign and read and comprehend the message while attending to the complex driving situation. Message familiarity enhances motorist reading time. When information displayed on a CMS applies to unfamiliar drivers, or when the information being presented to commuters is unusual, longer reading times will be required than for infor- mation posted frequently and seen repeatedly by commuting traffic. Site-specific characteristics and normal CMS operat- ing procedures dictate what information is usual and what is not, and therefore this factor varies from location to location. Another important consideration in designing CMS mes- sages is the need for motorists to time-share their attention to the roadway, to traffic, and to reading signs. Adults can read quite fast while sitting at home reading a newspaper or a novel Light-Emitting Diode* Fiber Optic Flip Disk Condition Meters Feet Feet FeetMeters Meters Sun: Mid-Day 244 800 244 800 183 600 Sun: Washout 244 800 244 800 122 400 Sun: Backlight 183 600 152 500 76 250 Nighttime 183 600 183 600 76 250 *Valid only for the newer aluminum indium gallium phosphide (or equivalent) LEDs. TABLE 1 LEGIBILITY DISTANCES FOR USE IN MESSAGE DESIGN AND DISPLAY ON CHANGEABLE MESSAGE SIGNS WITH 450-mm (18-in.) HIGH CHARACTERS (5â7)
10 70â80 km/h (45â50 mph) 90â105 km/h (55â65 mph) 115â120 km/h (70â75 mph) 130 km/h (80 mph) Daytime 4 units 4 units 4 units 3 units Daytime with Sun Behind Sign 4 units 3 units 3 units 2 units Nighttime 4 units 3 units 3 units 2 units *Valid only for the newer aluminum indium gallium phosphide (or equivalent) LEDs. TABLE 2 MAXIMUM NUMBER OF UNITS OF INFORMATION FOR USE IN MESSAGE DESIGN AND DISPLAY ON LIGHT EMITTING DIODE* AND FIBER OPTIC PORTABLE CHANGEABLE MESSAGE SIGNS WITH 450-mm (18-in.) HIGH CHARACTERS (5â7) UNIT OF INFORMATION Question Answer Unit of Information 1. What happened? ACCIDENT 1 unit 2. Where? PAST ROWLAND 1 unit 3. Who is advisory for? FAIR PARK 1 unit 4. What is advised? USE FITZHUGH 1 unit Exhibit 1 increased traffic conflicts (e.g., merging and lane changing), or climatological conditions, motorists will attend to those information needs they believe are most important to them and to their safety. These demands on the motorist will result in less time available to read the CMS message. In addition, lighting and environmental conditions affect CMS legibility. For example, during part of the day, the sun may not affect the legibility of the CMS. However, if the sun shines directly in the eyes of the motorist, then the legibility distance for the motorist can be greatly reduced. It may be necessary to reduce the length of the message to account for the reduced visibility. The CMS message designer should always look for ways to reduce the message length without losing the intent of the message. Reducing message length can sometimes be accom- plished by using alternative phrases that are understandable by motorists and have the same meaning as the original phrase. Also, there may be redundant or unimportant information in the message, which can be omitted. Message Load and Units of Information The term load refers to the units of information in the total message. A unit of information (or informational unit) refers to the answer to a question a motorist might ask. Stated an- other way, a unit of information is each data item in a message that a motorist could use to make a decision. Each answer is one unit of information. The incident message in Exhibit 1 has four units of information and serves to illustrate the con- cept of units of information. A typical unit of information is one to three words, but can be up to four words. Because motorists can process a limited amount of information, the amount of information that should be displayed on a CMS is also limited. Too much informa- tion, particularly when the driving situation is complex, can result in driver information overload. Driver information over- load results from providing too much information through devices or conditions for a driver to respond properly (14). When drivers are confronted with more information than they can process, they may decelerate severely or drive unduly slowly, make late or erratic maneuvers, take an improper route alternative, ignore critical information, fail to monitor other traffic, or have excessive eyes-off-the-road episodes. Research results indicate that drivers need 2 s per unit of information to be able to read, comprehend, and react to CMSs messages. The maximum number of units in a message is influenced by the legibility distance of the CMS and the operating speed on the freeway. Tables 2 and 3 contain information on the maximum number of units of information that should be displayed on LED, fiber optic, and flip disk CMSs (the most common types of CMSs) with characters that are 450 mm (18 in.) high (5â7). The recommendations shown in Tables 2 and 3 are based on research and operational experience (8â13). In addition, the following principles apply (5â7): â¢ No more than four units of information should be in a message when the traffic operating speeds are 56 km/h (35 mph) or more.
11 â¢ No more than five units of information should be dis- played when the operating speeds are less than 56 km/h (35 mph). â¢ No more than three units of information should be dis- played in a one message phase. â¢ No more than two units of information should be displayed on a message line. Message Format Message format refers to the order and arrangement of the units of information on a CMS. The CMS message must con- tain the proper information in the expected order to allow motorists to easily read and interpret the information and make rational decisions based on that information. Message Splitting Occasionally, the required message may be too long to dis- play on three CMS lines. Under this circumstance, a long message may be broken (chunked) into phases with compat- ible informational units. The MUTCD specifies that for free- way and expressway applications, no more than two phases should be used to display a CMS message (1, Â§2E21). To ensure that drivers are not overwhelmed with long messages, some state DOTs and TMCs have found it more effective to restrict CMS messages to three lines, and they do not use two-phase messages. Dynamic Features on Changeable Message Signs Experience has shown that some state DOTs use dynamic features on CMSs (i.e., flashing the message, flashing one of the lines in a message, or alternating one of the lines of a two- phase message) with the belief that the dynamic feature will attract the attention of drivers. Research reported by Dudek et al. (15, 16) indicated that these dynamic features should not be used. Using a driving simulator, Dudek et al. con- ducted studies to determine the effects of (1) flashing a one- phase, three-line message; (2) flashing one line of a one-phase, three-line message; and (3) alternating one line of a two-phase, three-line sign while keeping the other two lines constant between the phases (redundancy). In the first dynamic fea- ture, all three lines were flashed. Only the top line was flashed for the second dynamic feature. Messages with these three dynamic features were compared with comparable sta- tic messages. The measures of effectiveness were reading times, comprehension, and preference. In addition, driver performance measures of effectiveness were acceleration noise (an indication of the number and degree of speed changes), average lane position, standard deviation of lane position, average distance headway, maximum distance head- way, minimum distance headway, and standard deviation of distance headway. No differences in average reading time were found between the messages in which all three lines flashed and static mes- sages. However, the results suggested that flashing an entire one-phase message may have adverse effects on message understanding for drivers who are unfamiliar with this dynamic mode of display. A significant percentage of the subjects pre- ferred the static display. The average reading time for the flashing line (top line) messages was significantly longer than the static messages. The results also suggested that unfamiliar drivers will be ad- versely affected by this particular display feature, relative to comprehension of the entire message. The subjects liked the flashing line and static messages equally as well. The average reading time for the alternating line messages (with redundancy) was significantly longer than that for the messages that did not alternate (no redundancy). There was no significant difference in comprehension of each message line or for the number of message lines recalled. However, slightly less than 70% of subjects understood all four message lines for both message modes. CHANGEABLE MESSAGE SIGN OPERATIONS POLICIES A distinction is made between CMS operations policies and guidelines. CMS operations policies contain the guiding principles that are considered to be prudent and that influence the actions taken by the managers of TMCs in the operation of CMSs (e.g., the determination that CMSs should or should 70â80 km/h (45â50 mph) 90â105 km/h (55â65 mph) 115â120 km/h (70â75 mph) 130 km/h (80 mph) Daytime 4 units 3 units 3 units 2 units Daytime with Sun on Sign Face 3 units 2 units 2 units 2 units Daytime with Sun Behind Sign 2 units 1 unit 1 unit 1 unit Nighttime 2 units 1 unit 1 unit 1 unit TABLE 3 MAXIMUM NUMBER OF UNITS OF INFORMATION FOR USE IN MESSAGE DESIGN AND DISPLAY ON FLIP DISK PORTABLE CHANGEABLE MESSAGE SIGNS WITH 450-mm (18-in.) HIGH CHARACTERS (5â7)
not be blank when there are no incidents or roadwork on the freeway). CMS guidelines outline and describe the day-to- day operation of the CMSs (e.g., the content and format of CMS messages). Available information on guidelines was presented at the beginning of this chapter. Suggested polices that can be adopted by state DOTs for CMS operations are presented in previous research (5â7). There are no written CMS operations policies at the national level. However, policies, standards, and guidance are embodied in the MUTCD (1) and in four FHWA policy memoranda (17â20). In addition, another mem- orandum (21) describes FHWAâs recommendation for dis- playing travel time on CMSs. These FHWA memoranda are briefly described in the section that follows. FHWA Policies and Guidelines Use of CMSs Use of Changeable Message Signs (CMSs) (17), an FHWA policy memorandum dated January 19, 2001, supports use of CMSs as a traffic control device to safely and efficiently manage traffic by informing motorists of roadway conditions and the required actions to perform. The primary sections addressing CMSs in the MUTCD are Section 2A.07 Change- able Message Signs; Section 2E.21, Changeable Message Signs; and Section 6F.55, Portable Changeable Message Signs. Excerpts of the January 19, 2001, memorandum that relate to policies and guidelines follow: . . . Section 2A.07 of the Manual on Uniform Traffic Control De- vices (MUTCD) requires that a CMS shall conform to the prin- ciples established in the MUTCD related to the use of signs within the right-of-way of all classes of public highways, and to the extent practical, the design and applications prescribed in Sections 6F.02 and 6F.52 (now Section 6F.55). Section 2E.21 of the MUTCD specifies that âChangeable message signs shall dis- play pertinent traffic operational and guidance information only, not advertising.â The FHWA supports the use of a CMS as a traffic control de- vice to safely and efficiently manage traffic by informing motorists of roadway conditions and required actions to per- form. The appropriate use of a CMS and other types of real- time displays should be limited to managing travel, controlling and diverting traffic, identifying current and anticipated road- way conditions, or regulating access to specific lanes or the entire roadway. . . . The use of a CMS for the display of general public infor- mation or other nonessential messages is discouraged. Only essential messages should be displayed on a CMS. The content of a CMS message should be based on requiring the motorist to take an action. However, operational, road condi- tion, and driver safety focused messages are acceptable to be displayed on a CMS. If driver safety focused messages are to be displayed on a CMS, they should be kept current and relate to a safety campaign. The period of time that a specific message is displayed for a safety campaign should be limited to a few weeks . . . 12 Safety Campaign Messages âClick It or Ticketâ Signs, (18), an FHWA policy memorandum dated March 6, 2002, addresses whether the safety campaign message CLICK IT OR TICKET is in conformance with the MUTCD. Although the memorandum primarily addresses static signs, it implies that a CLICK IT OR TICKET message is appropriate for display on CMSs. The following statements are contained in this memorandum: The display of safety messages associated with a safety cam- paign is allowable under the current MUTCD, as long as it con- forms to sign design, location, and spacing requirements and does not block other regulatory, guide, and/or warning signs. We have determined that the âClick It or Ticketâ signs meet the design requirements and are in conformance with the Manual based on the following analysis. The Millennium Edition of the MUTCD does not specifically address safety message signs; however, there are provisions in Section 1A.03 and Section 2B.51 (now Section 2B.54) that allow an agency to develop its own regulatory and warning message signs, as long as they follow the basic guidelines on color, appearance, etc. Section 2B.51 (now Section 2B.54) of the Manual also includes the seat belt symbol. The Federal Highway Administration (FHWA) supports the use of a Changeable Message Sign (CMS) as a traffic control device to safely and efficiently inform motorists of roadway conditions and required actions to perform. The FHWA issued a policy memorandum on CMS January 19, 2001. That policy gives gen- eral guidance and allows driver safety messages to be displayed on a CMS including those associated with a safety campaign. The âClick It or Ticketâ sign design for a safety campaign con- forms to the information in this memorandum. AMBER Alert Messages AMBER AlertâUse of Changeable Message Sign (CMS) (19), a policy memorandum dated August 16, 2002, clarifies FHWA policy on the use of CMSs to display child abduction messages as part of an AMBER Plan Program. Parts of the memorandum that relate to policies and guidelines follow: If public agencies decide to display AMBER alert or child abduction messages on a CMS, FHWA has determined that this application is acceptable only if (A) it is part of a well- established local AMBER Plan Program, and (B) public agen- cies have developed a formal policy that governs the operation and messages that are displayed on CMS. (A) A local AMBER Plan Program would include written crite- ria for issuing and calling off an AMBER alert, procedures on issues to coordinate with local agencies and other inter- ests, and conforms to the recommendations of the national program. Specific criteria for issuing an alert and the asso- ciated procedures may include: 1. Confirmation that a child has been abducted; 2. Belief that the circumstances surrounding the abduction indicate that the child is in danger of serious bodily harm or death; and 3. Enough descriptive information about the child, abductor, and/or suspectâs vehicle to believe an immediate broad- cast alert will help.
13 (B) The formal public agency policy and procedures relating to displaying AMBER alert or child abduction messages on CMS must address the following issues: 1. The criteria under which CMS will be used for AMBER alerts. 2. Clear identification of the law enforcement agency re- sponsible for issuing the alert (e.g., state police, local police department, etc.). 3. Agencies, interests, and persons to be contacted and in- formation to be disseminated to initiate or call off an AMBER alert. 4. Specific recognition that traffic messages, such as lane closures, fog alerts, detours, etc., are the highest prior- ity, and circumstances under which the AMBER alert message could or could not be displayed. 5. Length of time to display the message (should be of short duration, typically a few hours). (Note: 4 and 5 should be defined in cooperation with the responsible law enforcement agency based on the specific circum- stances of the abduction.) 6. Geographic area over which the information is to be dis- played (should be limited to a reasonable search dis- tance that is reachable within a few hours). 7. Circumstances that would cause the discontinuation of use of the CMS if the AMBER alert message creates an adverse traffic impact such as queues, markedly slow- ing of traffic, etc. 8. Format and content of the messages to be displayed. Agencies should follow the recommended national CMS practices related to the development, use of text, manner in which messages should be displayed, and how CMS are operated. Emergency Security Messages Use of Changeable Message Sign (CMS) for Emergency Secu- rity Messages, (20) an FHWA memorandum dated March 21, 2003, contains documentation of FHWA policy for use of CMSs for emergency security. The part of the memorandum that addresses FHWA policy, should a public agency decide to display emergency or security alert messages on CMSs, follows: If public agencies decide to display emergency or security alert messages on a CMS, FHWA has determined that this application is acceptable if public agencies have developed policies and pro- cedures that govern the messages that are displayed on CMS and their operation. The public agency policy and procedures relat- ing to displaying emergency or security alert messages on CMS must address the following issues: 1. The criteria under which CMS will be used for emergency or security alert messages, including the necessary coordination with public safety or security agencies. Formal policies among critical stakeholders (such as law enforcement, secu- rity, transportation, and public safety) can be used to estab- lish these agreed upon criteria. 2. Protocols or hierarchy for prioritizing messages and deter- mining which messages are to be displayed. 3. Geographic area over which the information is to be dis- played, to be determined in cooperation with public safety and security agencies. 4. Identification of the circumstances under which transportation- related messages, such as lane closures, fog alerts, detours, or other messages that may be needed because of dangerous travel conditions in the immediate vicinity, would preempt emergency or security alert messages. 5. The criteria that would cause the discontinuation of use of the CMS if the emergency or security alert message creates an adverse traffic impact such as queues, markedly slowing traffic, etc. 6. Methodology for developing and displaying messages that are appropriate for CMS display including but not limited to standard message sets. Agencies should follow the recom- mended national CMS practices related to the development, use of text, manner in which messages should be dis- played, human factors related to understandability of the messages, and how CMSs are operated. Travel-Time Messages Information and Action: Dynamic Message Sign (DMS) Recommended Practice and Guidance, (21) an FHWA pol- icy memorandum dated July 16, 2004, notes that FHWA strongly recommends the display of travel-time information on CMSs whenever possible. A relevant part of the memo- randum follows: . . . Our goal should be to have travel-time information as the default information available to motorists throughout the day. A âdarkâ or blank CMS is a transportation investment that is not being fully utilized. We should be asking why is it dark and what will it take to get travel time posted on an ongoing basis. Fur- thermore, no new CMS should be installed in a major metropol- itan area or along a heavily traveled route unless the operating agency and the jurisdiction have the capability to display travel- time messages. State Department of Transportation Policies and Guidelines The TMCs were asked in the survey whether they have a written policy or guidelines regarding the design and/or display of CMS messages. Seventy-five percent of the TMCs that responded have a written policy or guidelines. The spe- cific agencies that reported having a written policy or guide- lines are listed here: â¢ Alabama DOT â¢ Arizona DOT â¢ California DOT (Caltrans) â¢ Colorado DOT â¢ Connecticut DOT â¢ Delaware DOT â¢ Georgia DOT â¢ Florida DOT â¢ Iowa DOT â¢ Kansas DOT â¢ Kentucky Transportation Cabinet â¢ Louisiana DOTD â¢ Maine DOT â¢ Maryland SHA â¢ Minnesota DOT â¢ Missouri DOT â¢ Nevada DOT â¢ New York State DOT â¢ North Carolina DOT
â¢ Oklahoma DOT â¢ Oregon DOT â¢ Pennsylvania DOT â¢ Rhode Island DOT â¢ South Dakota DOT â¢ Tennessee DOT â¢ Texas DOT 14 â¢ Utah DOT â¢ Virginia DOT â¢ Wisconsin DOT â¢ Harris County Toll Road Authority â¢ Illinois Tollway â¢ New Jersey Turnpike Authority, Turnpike Division â¢ Pennsylvania Turnpike Commission.